The Flattr WordPress plugin through 1.2.2 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup)
https://wpscan.com/vulnerability/2fb28c77-3c35-4a2f-91ed-823d0d011048/